Monolithic Microwave Integrated Circuits (MMIC) are implemented with conventional microstrip or grounded coplanar waveguide (GCPW) circuit elements on thin semiconductor substrates. The thickness of the substrate depends on the frequency of operation. Although at mm-wave frequencies wafer measurements of MMICs have shown satisfactory performance, MMICs actually suffer significantly in performance once removed from the wafer and packaged using either a ribbon bond approach or a flip-chip approach. The ribbon bond and flip-chip packaging approaches have a severe and detrimental effect on the performance of the MMICs at mm-wave frequencies.
At higher-mm-wave and sub-mm-wave frequencies, most of the measurement equipment and MMIC modules have waveguide Inputs/Outputs (I/Os). Researchers have demonstrated MMIC modules by coupling MMIC I/Os to waveguide using, either waveguide transitions or antennas. These transitions can be placed on a semiconductor substrate and ribbon bonded to the MMIC, as shown in FIGS. 1 and 2. However, transitions that have been placed on the MMIC semiconductor substrate degrade the MMIC module performance by introducing higher order parasitic modes because MMICs are developed on semiconductor materials like InP, SiGe, GaAs.
The transitions that have been designed on high performance substrates are ribbon bonded to the MMIC. Unfortunately, the assembly approach is complicated, MMIC module designs with ribbon-bonding suffer from impedance mismatch and produce lower power than expected, and at sub-millimeter frequencies, planar coupling transmission structures need to have narrow width for desired circuit impedances.
Transitions have also been integrated into the MMIC module. See Weinreb, S., Faier, T., Lai, R., Barsky, M., Leong, Y. C., and Samoska, L., “High-Gain 150–215-Ghz MMIC Amplifier with Integral Waveguide Transitions”, IEEE Microwave and Guided Wave Letters, Vol. 9, No. 7, pp 282–284, July 1999 (Weinreb). However; this approach still presents problems by introducing higher order modes. See FIG. 3.
The presently disclosed technology addresses the issues of higher order modes, parasitic modes, impedance mismatches by utilizing an integrated waveguide MMIC module quite unlike Weinreb. The presently disclosed technology eliminates or reduces the higher order modes in the waveguide by etching away extra high resistivity substrate around and/or underneath the coupling transmission structures. This allows the development of high-performance MMIC modules and subsystems at sub-millimeter and higher-millimeter wave frequencies.